The World Health Organization head and its chief scientist applauded Monday announcements by Pfizer and BioNTech that final stage trials of their vaccine have proven 90% effective in preventing COVID-19 infections.

"We welcome the encouraging vaccine news from @pfizer & @BioNTech_Group & salute all scientists & partners around the world who are developing new safe, efficacious tools to beat #COVID19," WHO Director-General Tedros Ghebreyesus tweeted.

US pharma company Pfizer and German biotech firm BioNTech issued a joint statement saying their "vaccine candidate was found to be more than 90% effective in preventing COVID-19 in participants without evidence of prior SARS-CoV-2 infection in the first interim efficacy analysis" in phase 3 clinical trials.

"The world is experiencing unprecedented scientific innovation & collaboration to end the pandemic," said Tedros on the day that the WHO main decision-making body, the World Health Assembly, began a hybrid meeting from Geneva.

Indexes in the US stock market and the price of crude oil soared Monday, with hopes of a successful vaccine candidate and Democrat Joe Biden becoming president-elect to end uncertainty in the 2020 election.

In mid-October, the WHO had identified 42 candidate vaccines at the final stage of clinical trials, up from 11 in mid-June.

The WHO's chief scientist Soumya Swaminathan also welcomed the two companies' announcements saying it should "encourage all developers of #COVID19 vaccines to continue with clinical trials."

"The world needs several safe, effective & affordable vaccines to end this pandemic," she said.

The WHO has said that it has 10 vaccines in the phase 3 stage.

It said: "Like all vaccines, COVID-19 vaccines should go through a rigorous, multi-stage testing process, including large (phase 3) trials that involve tens of thousands of people."

In a tweet Monday, WHO chief scientist Soumya Swaminathan said that the news from Pfizer and BioNTech should "encourage all developers of #COVID19 vaccines to continue with clinical trials."

Tedros, in a 40-minute speech to the WHA, said scientists know they need better tools to bring the pandemic under control by suppressing transmission and thereby saving lives.

He said WHO's partners Gavi, the vaccine alliance, CEPI to finance vaccines and the Global Fund, and the ACT Accelerator, or COVAX, support the development of vaccines and their fair distribution.

He said, "186 countries and economies are now participating in the COVAX facility."